It is a common problem in engines which have flat heads, and more particularly, flat aluminum heads, that overheating of the engine results in substantial warpage of the head rendering the engine unfit for usuage. When a head warps, it generally bows in the longest direction. This bowing usually takes the form of a convex bow of the head (when looking down upon the engine) and, because of the construction and the relative thickness of metal in the head, both the top and the bottom surface of the head which joins the engine block, bows or warps.
In these cases, the common practice is to discard the head and to reinstall a new head. There have however, been attempts to salvage the warped head by planing or milling the lower surface of the head to a flat surface in order to re-join in sealing relationship to the engine block. In these cases where the head bottom side is milled, and reassembled on the engine block, the problem still remains that the top of the head is still warped. As a consequence and in those cases where an overhead cam shaft is located on top of the head and then reinstalled in place, the cam bearings which are held in cam towers attached to the top of the head are no longer in straight alignment, but in fact continue the bow. This of course was the condition before the head was removed and after the head had originally been warped. The results of this non-alignment of the cam shaft bearing is to eventually, by excess pressure placed on different points of the cam shaft, to break the cam shaft or excessively wear the cam bearings so that the engine is rendered inoperable.
It is noted that even in referring to the manufacturer's official engine shop manuals for automobiles, that repairs of the engines for warped heads either takes the form of replacing the head or to mill and surface the lower surface of the head which comes into contact with the engine block.
Some mechanics and machine shops have learned, through experience, that indeed you must machine and prepare the surface of both the top and the bottom of the engine head if the same head having overhead cam shaft is to be placed back upon the block. However, in accomplishing this partially correct solution, an additional problem develops, which problem is remedied by the present invention.
When both the top and the bottom surfaces of the head are machined for flatness and parallel surfaces, this usually results in removing a considerable amount of metal, commonly a total exceeding 15/1000 to 20/1000 of an inch. In a great number of engines having the overhead cam shafts, the cam shaft rests upon cam towers, metal blocks which are attached to the top of the head and in which are secured the cam bearings. If the cam towers are replaced upon the head where an excess of 15/1000 inch of metal has been removed, the result is to bring the cam shaft chain sprocket closer to the chain sprocket attached to the engine crankshaft. Most engines have mechanisms in a form of idlers or other types of friction devices to adjust for slack in the timing chain connecting these two sprockets, however, it has proven to be the case in many engines that there is not sufficient adjustment to correct excess slack where the cam shaft sprocket and the crankshaft sprocket have been moved closer than 15/1000 inch from the original manufacturer's specification. As a result, rebuilding an engine after taking off an excess of 15/1000 inch total on both surfaces of the head results in excessive slackness in the timing chain and inability to achieve proper clearance between the valve stem ends and valve rockers.
Commonly then, at least 80% of the machine shops doing engine repair business will inform the owner of the engine that in the case of moderate to severe warped engine heads, that repairs cannot be made upon the head and that it is necessary that a new head be placed upon the engine block.
It is the rectification of this problem to which the present invention is directed.